FMCW/2FD implementation for vehicle near obstacle detection system

Abstract

A vehicle near obstacle detection system includes a plurality of radio frequency heads that can transmit and receive both frequency-modulated, continuous wave and two-frequency Doppler radar signals, such that the system operates in frequency-modulated, continuous wave radar mode and in two-frequency Doppler radar mode. The radio frequency heads used for transmitting the radar signals transmit their radar signals in accordance with commands from a system controller. The radio frequency heads are provided at various locations on the vehicle, directed at points around the vehicle which cannot easily be seen by the vehicle operator. The system controller switches between the two radar modes depending on which one is more appropriate to make use of one mode's strengths while avoiding the other mode's weaknesses. When there is no relative movement between objects and the vehicle, the frequency-modulated, continuous wave mode is used. When there is relative movement and the accuracy warrants it, the two-frequency Doppler mode is used.

We claim: 
     
       1. A vehicle near obstacle detection system, the system comprising: a radio frequency head capable of transmitting and receiving both frequency-modulated, continuous wave radar signals and two-frequency Doppler radar signals;   signal processing means responsive to received radar signals reflected from an object for determining the range to the object;   means for sensing vehicle speed; and   means for controlling the radio frequency head to (A) transmit frequency-modulated, continuous wave radar signals when the sensed vehicle speed is zero and (B) transmit two-frequency Doppler radar signals when at least the sensed vehicle speed is greater than zero.   
     
     
       2. A vehicle near obstacle detection system, the system comprising: a radio frequency head capable of transmitting and receiving both frequency-modulated, continuous wave radar signals and two-frequency Doppler radar signals;   signal processing means responsive to received radar signals reflected from an object for determining the range to the object; and   means for controlling the radio frequency head to (A) transmit frequency-modulated, continuous wave radar signals when the determined range is greater than a predetermined distance and (B) transmit two-frequency Doppler radar signals when the range is less than the predetermined distance.   
     
     
       3. A vehicle near obstacle detection system, the system comprising: a radio frequency head capable of transmitting and receiving both frequency-modulated, continuous wave radar signals and two-frequency Doppler radar signals;   signal processing means responsive to received a radar signals reflected from at least one object for determining the range to a nearest object when two-frequency Doppler radar signals are transmitted and for determining the ranges to multiple objects when frequency-modulated, continuous wave radar signals are transmitted;   means for sensing vehicle speed; and   means for controlling the radio frequency head to (A) transmit frequency-modulated, continuous wave radar signals in response to predetermined conditions including (b 1) the sensed vehicle speed is zero, (2) the determined range to the nearest object is greater than a predetermined distance and (3) radar signals are reflected from multiple objects while the radio frequency head is controlled to transmit frequency-modulated, continuous wave radar signals and (B) transmit two-frequency Doppler radar signals otherwise.   
     
     
       4. A method of detecting obstacles in proximity to a vehicle having a radio frequency head capable of transmitting and receiving both frequency-modulated, continuous wave radar signals and two-frequency Doppler radar signals, the method comprising the steps of: determining the range to an object from received radar signals reflected from the object;   sensing vehicle speed; and   controlling the radio frequency head to (A) transmit frequency-modulated, continuous wave radar signals when the sensed vehicle speed is zero and (B) transmit two-frequency Doppler radar signals when at least the sensed vehicle speed is greater than zero.   
     
     
       5. A method of detecting obstacles in proximity to a vehicle having a radio frequency head capable of transmitting and receiving both frequency-modulated, continuous wave radar signals and two-frequency Doppler radar signals, the method comprising the steps of: determining the range to an object from received radar signals reflected from the object; and   controlling the radio frequency head to (A) transmit frequency-modulated, continuous wave radar signals when the determined range is greater than a predetermined distance and (B) transmit two-frequency Doppler radar signals when the range is less than the predetermined distance.   
     
     
       6. A method of detecting obstacles in proximity to a vehicle having a radio frequency head capable of transmitting and receiving both frequency-modulated, continuous wave radar signals and two-frequency Doppler radar signals, the method comprising the steps of: determining the range to a nearest object from received radar signals reflected from the nearest object when two-frequency Doppler radar signals are transmitted;   determining the ranges to each object from received radar signals reflected from at least one object when frequency-modulated, continuous wave radar signals are transmitted;   sensing vehicle speed; and   controlling the radio frequency head to (A) transmit frequency-modulated, continuous wave radar signals in response to any one of predetermined conditions including (1) the sensed vehicle speed is zero, (2) the determined range to the nearest object is greater than a predetermined distance and (3) radar signals are received reflected from multiple objects while the radio frequency head is controlled to transmit frequency-modulated, continuous wave radar signals and (B) transmit two-frequency Doppler radar signals otherwise.